The invention relates to a device for the synchronization of a local clock signal with time spaced digital data bursts comprised by an information signal, the frequency of the data burst having a given relationship with the frequency of a continuous signal.
The development of digital optical disc technology has led to discs carrying audio and video signals, the audio signals being of the now-conventional Compact Disc (Trade Mark) standard, and the video signals being in particular high definition signals in accordance with the MAC standard, specifically D2-MAC. In accordance with the MAC standard digital data bursts corresponding to the audio channel (or channels) of the video signal are followed by time-multiplexed analog chrominance and luminance signals. To read such a carrier it is necessary to provide a synchronization between a local clock and the digital data bursts of the video signal.
Such a synchronization is not without problems. The frequency spectrum of the corresponding clock not only exhibits a central frequency in the present case 10.125 MHz, which would be the same if the information were present permanently, but also sidebands which are regularly spaced at opposite sides of the central band, in the present case at an interval of 15.625 Hz, and which arise because the information takes the form of spaced-apart bursts.
The rotation of the disc is controlled with a certain accuracy, which manifests itself as a frequency shift of maximum 28 kHz. As a result of this a conventional synchronization control system may lock at random to the desired central frequency as well as to some of the sidebands, in the present case at least four, in which last-mentioned case it will be impossible to recover the information.